HR: 0800h
AN: T11C-0739    [Abstracts]
TI: Dynamic Effects of Long-Wave Density Gradients due to Internal Heating
AU: * Morris, S
EM: morris@me.berkeley.edu
AF: Mechanical Engineering, University of California, Berkeley, CA 94720, United States
AB: Though it is estimated that 50--80% of the heat lost from the earth is generated internally within the mantle, our conceptual picture of mantle flow is based on simplified boundary layer models for bottom heated convection, in which the temperature is adiabatic outside thin boundary layers, and the flow is driven purely by the excess mass of cold plumes (subducting slabs). That picture underlies simplified models in which mantle flows are calculated from horizontal density gradients inferred from seimology. As a reminder of the assumptions underlying that approach, we give a solution of the coupled fully nonlinear Boussinesq equations describing horizontal flow in a horizontal layer of viscous but thermally non--conducting fluid with uniform internal heating. The shear stress and heat flux both vanish at the top and bottom of the layer; the flow is driven purely by the small-- amplitude long--wave baroclinicity due to internal heating, and heat generated internally is removed by the purely horizontal flow. This solution models flow near the centre of a large--aspect ratio convection cell, like that occurring beneath the Pacific plate. (There, heat generated internally is first transported horizontally over the cell length, then removed at the cell end by mixing of the heated material with the cold subducted slab. Our solution models only the first of those processes.) Although our solution does not contain a cold plume, it predicts that the small--amplitude long--wave density field due to internal heating can, by itself, generate velocities close to those observed. Simplified mantle flow models that assume the motion to be driven purely by seismically observable density differences across slabs may be ignoring an essential part of the forcing. Morris, S. J. S. GRL, 34,doi:10.1029/2007GL030059
DE: 7270 Tomography (6982, 8180)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8130 Heat generation and transport
DE: 8155 Plate motions: general (3040)
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting